The present invention relates to a timepiece having:
an electrical energy generator comprising a rotor and means for supplying electrical energy in response to rotation of the rotor; PA1 a source mechanical energy mechanically coupled to the rotor to cause rotation of the rotor at a speed greater than a set desired speed; and PA1 slaving means for slaving the rotational speed of the rotor to the desired speed which is energized by the electrical energy and which includes: PA1 measuring means coupled to the generator for producing a plurality of measurement pulses, each of the measurement pulses being produced in response to the rotor travelling through a particular angular position; PA1 reference means for producing a plurality of periodic reference pulses having a period equal to that of the measurement pulses when the rotor is rotating at the desired speed; PA1 comparing mean for supplying a comparison signal representative of the difference between, on the one hand, a first number which is the number of the reference pulses that are produced as from a determined initial instant and, on the other hand, a second number which is the number of the measurement pulses that are produced as from the determined initial instant, the comparison signal having a first state and a second state dependent on whether the first number is less than or, respectively, greater than the second number; and PA1 braking means responsive to a command signal for applying to the rotor a braking torque that imposes upon the rotor a, speed of rotation less than the desired speed. PA1 an electrical energy generator comprising a rotor and means for supplying electrical energy in response to rotation of the rotor; PA1 a source of mechanical energy mechanically coupled to the rotor to cause the rotor to rotate at a speed greater than a set desired speed; and, PA1 slaving means for slaving the rotational speed of the rotor to the desired speed, the slaving means being electrically connected to the generator to receive electrical energy therefrom and comprising: PA1 measuring means coupled to the generator for producing a plurality of measurement pulses, each of the measurement pulses being produced in response to the rotor travelling through a particular angular position so as to determine its actual angular position; PA1 reference means for producing a plurality of periodic reference pulses having a period equal to that of the measurement pulses when the rotor is rotating at the desired speed, the reference pulses being independent of the measurement pulses and being representative of a theoretical angular position of the rotor; PA1 comparing means for supplying a comparison signal representative of the difference between a first number, which is the number of the reference pulses that are produced from a determined instant, and a second number, which is the number of the measurement pulses that are produced from the determined instant, the comparison signal having a first state and a second state dependent on whether the first number is less than or greater than the second number respectively; PA1 braking means responsive to a command signal for applying to the rotor a braking torque that imposes upon the rotor a speed of rotation that is less than the desired speed, the braking means then short-circuiting the means for supplying electrical energy; PA1 and control means responsive to each of the measurement pulses only when the comparison signal is in the first state to produce a command signal in the form of a command pulse of fixed duration so that the braking means only applies a braking torque to the rotor when the latter is leading with respect to the theoretical angular position.
A timepiece having these features, described for instance in U.S. Pat No. 3,937,001, has the same accuracy as a conventional electronic timepiece because the reference pulses, whose frequency determines the rotational speed of the generator's rotor and hence of the hands displaying the ongoing time, are produced from a signal supplied by a quartz oscillator.
Further, this timepiece has neither cell nor accumulator since its electronic circuits are energized by the electrical energy provided by its generator whose rotor is connected to its source of mechanical energy, formed by a barrel spring similar to that used in conventional mechanical timepieces.
This represents a clear advantage in relation to a conventional electronic timepiece whose circuits are supplied by a cell or an accumulator, which have a limited life.
In the timepiece described in U.S. Pat. No. 3,9373,001, mentioned above, the means for braking the generator's rotor are formed by a resistor connected in series with an electronic switch, the arrangement formed by this resistor and this switch being connected in parallel with the generator's coil.
Further, this switch is controlled directly by the comparison signal so as to be permanently closed when the latter is in its first state, i.e. as long as the generator's rotor is ahead with respect to the position it would have occupied had it always been rotating at its desired speed.
It may therefore happen for this rotor to be braked without interruption for quite a long time, particularly if it had before been strongly accelerated by an angular shock.
The electronic circuits of the timepiece are energized by a d.c. voltage supplied by a circuit for rectifying the a.c. voltage produced by the generator.
The value of this d.c. voltage, which depends on the value of this a.c. voltage, must obviously be at all times sufficient for these electronic circuits to operate properly.
Now when the generator's rotor is braked, the lower the braking resistance, the lower the a.c. voltage produced by the generator, that a.c. voltage being obviously nil if the braking resistance is itself nil.
If the generator's rotor were braked for only relatively short periods of time, the electronic circuits of the timepiece could be energized, during these braking periods, by the electrical energy that has accumulated in the capacitor or capacitors generally comprised by the rectifier circuit energizing these circuits, even if the value of the braking resistance were nil.
But, as explained above, the generator's rotor may be braked without interruption for quite a long period of time. It is therefore practically out of the question to choose a nil value for the braking resistance because the capacitor of the rectifier circuit would then have to have a very large capacitance and would therefore be rather bulky and expensive. Besides, it would not be possible to ascertain for sure the capacitance the capacitor should have since the maximum length of time during which the generator's rotor may be braked cannot be anticipated.